1. Field of the Disclosure
The present invention relates to a pressure actuated switching device and a system and method for making it. It especially relates to the use of green rubber to fabricate a tubular sensor with a highly conductive elastomer coating within the channel of the sensor.
2. Description of the Related Art
Pressure actuated switching devices are known in the art. Typically, such devices include two spaced apart conductive layers enveloped in an insulative outer cover. Optionally, the conductive layers may be separated by an insulative spacer element, or xe2x80x9cstandoff.xe2x80x9d Also, the pressure actuated switching device can optionally include a piezoresistive material. The electrical resistance of a piezoresistive material decreases in relation to the amount of pressure applied to it. Piezoresistive materials provide the pressure actuated switching device with an analog function which not only detects the presence of a threshold amount of applied force but also provides a measure of its magnitude. Pressure actuated switching devices can be used as mat switches, drape sensors, safety sensing edges for motorized doors, and the like.
U.S. Pat. Nos. 6,121,869 and 6,114,645 to Burgess disclose a pressure activated switching device which includes an electrically insulative standoff positioned between two conductive layers. The standoff is preferably a polymeric or rubber foam configured in the form of contoured shapes having interdigitated lateral projections. Optionally the switching device can include a piezoresistive material positioned between a conductive layer and the standoff.
U.S. Pat. No. 5,856,644 to Burgess discloses a freely hanging drape sensor which can distinguish between weak and strong activation of the sensor. The drape sensor includes a piezoresistive cellular material and a standoff layer. The drape sensor can be used in conjunction with moving objects such as motorized doors to provide a safety sensing edge for the door. Alternatively, the drape sensor can be used as a freely hanging curtain to detect objects moving into contact therewith.
U.S. Pat. Nos. 5,695,859, 5,886,615, 5,910,355, 5,962,118 and 6,072,130, all to Burgess, disclose various embodiments of pressure activated switching devices.
There is a special need for a narrow channel tubular sensor switch to serve as a backup obstacle detector on the lift gate, or rear hatch, of automotive vans or mini-vans. This backup obstacle detection device is preferably in the form of a seal type touch strip attached to the vehicle body or door panel, where the door closure will create a small area that could trap objects as the door is closing. For example, lift gates or rear hatches which close with a scissors-like action create very small spaces where the door moves toward the body.
As demand grows for lower cost high performance elongated narrow channel tubular pressure actuated switches, it becomes increasingly advantageous to fabricate these devices from high functioning rubber materials and to have more efficient and more flexible related methods of production. For example, it may be preferable to have one or more components fabricated more efficiently at one facility or operation, then shipped to another facility or operation for further processing and/or assembly. These and other advantages are provided by the system and method for making a high quality simplified rubber pressure actuated switching tubular device as described below. The desired narrow channeled tubular sensor meets the rigid all weather requirements of the transportation and other industries.
It is an object of this invention to create an inexpensive, but high performing narrow elongated channel tubular sensor switch and system and method of manufacturing the switch. A further object of the present invention is to provide several variations of tubular sensor configurations with related methods of manufacturing designed for a variety of applications.
The object of the present invention is achieved, in broad terms, providing an elastomer or rubber tubular shaped switch form, through special processing from green rubber, to effect a housed, vulcanized, integrated conductive coated electrode, switch sensor. Several variations of high quality tubular sensor configurations and related systems and methods for making a pressure actuated switching device is provided herein. The system includes the steps of: (a) providing at least a first strip sheet of green rubber material; (b) applying at least a first layer of fluid conductive green rubber polymeric coating material to at least a portion of a surface of the first strip sheet of green rubber material; (c) drying or solidifying the first conductive polymeric coating; and, (d) providing at least a second strip sheet of green rubber material; (e) applying at least a first layer of fluid conductive green rubber polymeric coating material to at least a portion of a surface of the second strip sheet of green rubber material; (f) drying or solidifying the first conductive polymeric coating; and, (g) elongated channel forming of the first coated layer of green rubber (coating facing outward); (h) with second layer of green rubber (coating facing inward) mating to merge pinch the edges together; (i) vulcanizing the mated sheets of green rubber material to form a cross-linked elastomeric tubular substrate.